1. Technical Field
The present invention relates to a transmitter in a mobile communication system that uses a communication system such as Wide band-Code Division Multiple Access (W-CDMA) to perform radio communication, and particularly relates to a technique for detecting peak power occurring in a transmission signal and suppressing the peak power.
2. Background Art
A transmitter has peak power suppression means to detect peak power occurring in a transmission signal and suppress the peak power (for example, refer to patent document 1).
FIG. 13 shows an example of an internal configuration of peak power suppression means 203.
Power calculating means 211 calculates a power value for each sample for an input signal. Peak power detection means 212 compares a power value of the input signal to a threshold power value being set for each sample, and determines a sample having a larger power value than the threshold power value as peak value. Peak suppression ratio calculating means 213 obtains a ratio between a peak power value and the threshold power value, and calculates a certain ratio (peak suppression ratio) for suppressing the peak power to a threshold level. Window function multiplication means 214 multiplies the peak suppression ratio by a window function beforehand stored in a memory, and determines a suppression ratio to the peak power and samples around the peak power.
When the peak power is continuously detected, a peak power having a maximum level in the continuous peak power is selected and multiplied by the window function. Thus, peak power around the maximum peak is also suppressed well.
As the window function w(t), for example, Hanning window as expressed by formula (1), Gaussian window as expressed by formula (2), and Kaiser window as expressed by formula (3) are known, and an optimum window that provides an excellent characteristic can be selectively used.
                    Formula        ⁢                                  ⁢        1                                                                                  Hanning            ⁢                                                  ⁢            window            ⁢                          :                        ⁢                                                  ⁢                          w              ⁡                              (                t                )                                              =                      0.5            +                          0.5              ⁢                              cos                ⁡                                  (                                      π                    ×                                          t                                              N                        /                        2                                                                              )                                                                    ⁢                                  ⁢                  however          ,                                    -                              N                2                                      ≤            t            ≤                          N              2                                      ⁢                                  ⁢        N        ⁢                  :                ⁢                                  ⁢        number        ⁢                                  ⁢        of        ⁢                                  ⁢        samples        ⁢                                  ⁢        of        ⁢                                                  ⁢                                                ⁢        window        ⁢                                  ⁢        function                            formula        ⁢                                  ⁢                  (          1          )                                        Formula        ⁢                                  ⁢        2                                                                                  Gaussian            ⁢                                                  ⁢            window            ⁢                          :                        ⁢                                                  ⁢                          w              ⁡                              (                t                )                                              =                                    ⅇ                                                -                  α                                ⁢                                                                  ⁢                                  t                  2                                                      ⁡                          (                              α                ⁢                                                                  ⁢                is                ⁢                                                                  ⁢                constant                            )                                      ⁢                                  ⁢                  however          ,                                    -                              N                2                                      ≤            t            ≤                          N              2                                      ⁢                                  ⁢                  N          ⁢                      :                    ⁢                                          ⁢          number          ⁢                                          ⁢          of          ⁢                                          ⁢          samples          ⁢                                          ⁢          of          ⁢                                          ⁢          window          ⁢                                          ⁢          function                                    formula        ⁢                                  ⁢                  (          2          )                                        Formula        ⁢                                                  ⁢                                                ⁢        3                                                                                  Kaiser            ⁢                                                  ⁢            window            ⁢                          :                        ⁢                                                  ⁢                          w              ⁡                              (                t                )                                              =                                                    I                0                            [                              α                ⁢                                                      1                    -                                                                  (                                                                                                                                                                              1                                  -                                                                                                                                                                                                                      2                                  ⁢                                                                      (                                                                          t                                      +                                                                              N                                        /                                        2                                                                                                              )                                                                                                                                                                                N                                                )                                            2                                                                                  ]                                                      I                0                            ⁡                              (                α                )                                                    ⁢                                  ⁢                                            I              0                        ⁡                          (              α              )                                =                      1            +                                          ∑                                  m                  =                  1                                M                            ⁢                                                [                                                                                    (                                                  α                          /                          2                                                )                                            m                                                              m                      !                                                        ]                                2                                                    ⁢                                  ⁢                  (                      α            ,                          M              ⁢                                                          ⁢              is              ⁢                                                          ⁢              constant                                )                ⁢                                  ⁢                  however          ,                                    -                              N                2                                      ≤            t            ≤                          N              2                                      ⁢                                  ⁢                  N          ⁢                      :                    ⁢                                          ⁢          number          ⁢                                          ⁢          of          ⁢                                          ⁢          samples          ⁢                                          ⁢          of          ⁢                                          ⁢          window          ⁢                                          ⁢          function                                    formula        ⁢                                  ⁢                  (          3          )                    
A windowing multiplier 215 multiplies the peak suppression ratio multiplied by the window function and an input signal together for each sample so as to generate a peak suppression signal having a frequency band being controlled to be in a neighborhood of a carrier by windowing. A subtractor 216 subtracts the peak suppression signal from a transmission signal (input signal), thereby suppresses peak power in the transmission signal to a set threshold level.
Patent document 1
JP-A-2005-20505